1. Field of the Invention
The present invention is directed to an X-ray diagnostics installation of the type having an X-ray source, an X-ray image intensifier, a video camera, control means for generating control pulses for the acquisition of images, and subtraction means for forming the difference between stored video signals and continuous, current video signals under the same exposure conditions. Such X-ray diagnostics installations serve the purpose of marking vessels in a radiograph according to the so-called pathfinder technique.
2. Description of the Prior Art
European Application 0 193 712, corresponding to U.S. Pat. No. 4,709,385, discloses an X-ray diagnostics installation of the above general type, wherein images of a complete heart cycle are entered into an image memory as a mask scene under ECG control. The stored video signals of the vessel system belonging to the same heart phase can thereby be superimposed on the current video signal in fluoroscopic mode. Such an apparatus is utilized in the pathfinder technique.
This pathfinder technique is employed in cardiac angiography so that the examining person can recognize the course of a catheter after introduction thereof into the vessel paths, even without a contrast agent. To this end, the ongoing, dynamic fluoroscopic image that shows the catheter is superimposed with the vessel representation generated by subtraction angiography. As a result, the examining person recognizes the course of the vessels and can correspondingly control the catheter. A spatial recognizability of subtraction images in the fluoroscopic mode, however, is not possible.
It is known that an X-ray diagnostics installation of the above general type can produce displayed images having improved depth appearance by operation in a two-level or two-plane mode or using stereo irradiation of the subject. An undesirably high outlay, however, is necessary for this purpose since, for example, two X-ray systems must be employed given a two-plane mode. In an X-ray stereo apparatus disclosed in German PS 35 20 917, two X-ray sources arranged laterally next to one another are operated in alternation. The X-ray images are successively read into image memories, so that an X-ray stereo pair is contained therein, this pair being supplied to the respective eyes of an observer via two separate monitors. Increased outlay occurs as a result of the stereo reproduction means and, moreover, the observation means required, for example polarization eyeglasses, limit the field of vision of the examining person.